Ink-spread compensated bar code symbology and compensation methods

ABSTRACT

A method for producing an ink-spread compensated variant of an existing optical code encodation scheme, wherein the existing encodation scheme has printed areas and spaces having a length in at least one dimension being a function of a given unit length for encoding information. In the method, the pattern of printed areas and spaces for a given data input is determined and a given length is added to the length of each space while the length of the printed areas remains unchanged to enlarge the overall length of the resulting code symbol in the at least one dimension.

CROSS-REFERENCE(S) TO RELATED APPLICATIONS

This application is a continuation application of application Ser. No.10/013,400, filed Dec. 10, 2001, which claims priority under 35 U.S.C §119 to U.S. Provisional Application Ser. No. 60/256,007, filed on Dec.15, 2000 and entitled “Ink-Spread Compensated Bar Code Symbology AndCompensation Methods,” the entire contents of which is expresslyincorporated herein.

FIELD OF THE INVENTION

The present invention relates to a new method of pre-compensating forink spread (often called “print gain” or “dot gain”) before printing abar code or binary code.

BACKGROUND

There are two encodation schemes commonly used in modem bar codesymbology design, “Binary” encoding and (“n,k)” encoding. Each havetheir advantages and disadvantages; generally speaking, (n,k) encodingis more space-efficient, but Binary encoding is more tolerant of poorprinting. Thus, both types will continue to be widely used for theforeseeable future. “Binary” codes (such as Code 39) define the set ofbar/space patterns making up its “language” or bar code character setusing only two choices (“wide” or “narrow”) for each bar and space ofeach pattern. The wide:narrow ratio can be selected when printing eachbar code. Selecting a 2:1 ratio creates a more compact bar code; a 2.5:1or 3:1 ratio makes the bar code wider, but also makes it easier for thescanner to distinguish wide elements from narrow ones (helpful whenprinting on rough cardboard, for example). “Delta Distance” codes (Suchas UPC-A and Code 128) use an encodation scheme known as (n,k) encoding,to define the set of bar/space patterns making up its “language” or barcode character set. In an (n,k) code, each bar code character iscomprised of “k” bars and “k” spaces (eg, 3 bars and 3 interleavedspaces), and each individual bar and space is an integer multiple (1,2,. . . m) of a unit width (called a “module”). Unlike the case for Binarycodes, these ratios cannot be altered to accommodate difficult printingsituations.

One characteristic that the Binary and (n,k) encodation schemes share isthat they both define a unit width (called a module), and in eitherscheme, the narrowest bars and the narrowest spaces are both one modulewide. Ideally, every printed barcode would be printed exactly tospecification, in order to allow a maximum tolerance for noise and otherdistortions during the scanning process. In practice, however, theprinting process can introduce a variety of imperfections, many of theseresulting from imperfections in the paper (or other substrate) that thebar code is printed upon. These substrate imperfections may introducerandom errors in the positions of the edges that separate dark bars fromlight spaces within the bar code.

One substrate-induced error stems from the fact that differentsubstrates vary (and even different pages of the same substrate vary) inhow they absorb ink at the time of printing. The result is that, on agiven sample of a substrate, the dark areas (bars) of a bar code may besignificantly wider than the spaces that were nominally of the samewidth. Yet, on a different sample, the same bar code digital image mayresult in a printed symbol where the bars are narrower than nominal,rather than wider. It is usually the case, however, that on a givenprinted sample, all of the printed dots tend to show the same amount of“dot gain” (or loss). Therefore, all of the bar code's bars tend to beeither bigger than nominal (and by the same amount), or all are smaller(and by the same amount). Thus, from the perspective of reading a barcode, this dot-gain phenomenon is considered a systematic (not random)error, and is known as “uniform ink spread.”

Uniform ink spread is such a common printing problem that currentsymbology designs almost always rely on a technique called “edge tosimilar edge decoding” (also called “delta distance decoding”) to handleit. Ink spreads uniformly outwardly from the center of each printed dot,and therefore the left and right edges of every printed bar will moveoutwardly (from the bar's center) by equal amounts. Thus, a measurementtaken from the left edge of one bar, across the bar and the next space,to the left edge of the next bar, will not vary with the degree of inkspread. Some bar code symbologies, such as Code 128, were designed to bedecoded based on such “edge to similar edge” measurements and thus arerelatively immune to uniform ink spread.

Unlike codes such as Code 128, binary codes are typically not decodedusing “delta distance decoding” techniques and thus do not have the sameinherent immunity to ink spread. However, various techniques fordecoding binary codes (by estimating a “threshold” width, ideallyhalfway between the nominal wide and nominal narrow widths) are wellknown in the art, and can provide good immunity to ink spread and otherprinting errors.

Although “delta distance decoding” and other decoding techniques knownin the art address some problems caused by ink spread, there is aremaining problem with ink spread that is not solved by thesetechniques. This problem is that when narrow (1-module) spaces shrinkdue to ink spread, they can become so narrow that they may not be seenat all by the scanner (or at the least, will reduce the effectiveworking range of the scanner). So, even with “delta distance” codes,some form of ink spread control is required. This is done by adjustingthe ideal representation of the bar code before printing it, a processoften known as “pre-compensation” of the image.

Traditional ink-spread pre-compensation methods involve reducing thewidth of each printed bar with an exactly corresponding increase in thewidth of each space (or the opposite—increasing the bar width anddecreasing the space—in those rare cases where the expectation is for aconsistently under-inked printing process). For example, one mightadjust the ideal bar code image by replacing the last column of blackpixels of every bar with a column of white pixels (i.e., “shaving” onedot from the right edge of every bar). The advantage of this traditionalapproach is that the decoding technique, as described above, gives anidentical edge-to-similar-edge measurement, whether compensation wasapplied or not. The major disadvantage is that, by definition, the barcode image contains bars that are less than 1 module wide. This createstwo significant problems.

First, if, in a given instance of printing, the ink does not spread, theprinted code will have bars that are smaller than nominal. Thiscondition can degrade scannability. Similarly, if the ink-spreadphenomenon is not consistent from one printed sample to another, thenthe traditional pre-compensation method will sometimes improve systemperformance, and sometimes degrade it.

Second, the compensated image now contains “finer” lines than before. Itis common for the same page-layout file to be used for printing onpresses with different physical resolutions (i.e., the physical distancebetween dots of the printer vary significantly across printingprocesses). The last step in the publishing chain, called Raster ImageProcessing, maps the image to the addressable dots of the printer. Thisstage, and previous stages, can introduce rounding or scaling errors inthe widths of the bars and spaces. The thinner the bars, the more likelythat the process will create an occasional bar that is much too wide ornarrow, resulting in an unreadable barcode.

Thus, in order to avoid both of these problems, the idealpre-compensation method would not decrease the size of any bars orspaces of the bar code.

The use of bar codes in printed advertisements and newspaper text isexpected to increase significantly in the near future, as the cost ofInternet-enabled scanning devices becomes low enough for the consumermass market. Currently, several methods have been proposed for using aprinted bar code for automatically connecting to an appropriate site onthe World Wide Web. As a result of this and other applications, it willbecome increasingly common to print the same bar code image, and thesame advertisement containing a bar code image, in a variety of printmedia including magazines, newspapers, catalogs, and telephonedirectories (white pages and yellow pages). Each of these print mediatypically has its own combination of printing press technology (such asgravure, offset, and flexography) and paper (ranging from high-weightglossy paper in magazines, to recycled newsprint and the very low-weightpaper used in a telephone book), each variation of which may havedifferent ink spread characteristics. Therefore, as consumer scanningapplications proliferate, it will no longer be feasible to generate asingle bar code image, or a single ad containing a bar code, that willbe appropriately pre-compensated for all of the substrates it will beprinted on, using traditional pre-compensation techniques.

SUMMARY OF THE INVENTION

A main object of the present invention is to provide a method for printgain compensation that does not reduce the widths of any elements of abar code or binary code.

Another object of the present invention is to provide a bar codesymbology, where the ideal image of the bar code does not requirefurther compensation for ink spread or reduction, and therefore is moresuitable than current symbologies for printing in a wide variety ofpress processes, to a wide variety of paper and other substrates.

A further object of the present invention is to provide a method forprint gain compensation by designing a symbology that does not containany spaces as small as the nominal narrowest bar width, so as tominimize the negative effects of ink spread.

Yet another object of the present invention is to provide a bar codesymbology, where the reading system can automatically discriminatebetween the standard version of the symbology, and one or more versionsthat have been pre-compensated for print gain using the techniques ofthe present invention.

Yet a further object of the present invention is to provide a method fordecoding a pre-compensated symbology.

These and other objects and advantages of the present invention areachieved in accordance with the present invention in whichpre-compensation is applied to an existing optical code encodationscheme wherein the digital image of the code increases the width of thespaces, but does not reduce or increase the widths of the bars. Inparticular, and in accordance with one embodiment of the method of thepresent invention, the pattern of printed areas and spaces for a givendata input is determined and a given length is added to the length ofeach space while the length of the printed areas remains unchanged toenlarge the overall length of the resulting code symbol in the at leastone dimension.

The resulting bar code image will result in a robust printed symbol,even if the final printing stage introduces no dot gain, or evenexhibits dot loss rather than dot gain. The method according to thepresent invention, while particularly suitable for bar codes and inparticular for n,k bar codes, can be used with other types of opticalcodes, such as binary codes, that suffer from ink spread problems.

The existing optical code symbology is preferably a bar code having barsand spaces of varying widths and wherein the added given length is afunction of the width of the narrowest space. Preferably, the bar codeis an n,k bar code and wherein the added length is a function of amodule width of the resulting bar code symbol. In a preferredembodiment, the added length is x modules where 0<x≦2 and mostpreferably the added length is 0.5 or 1 module.

In a particularly commercially advantageous embodiment of the presentinvention, wherein the n,k bar code is an 11,3 bar code wherein the barsand spaces are from 1 to 4 modules in length. A bar code of this type isdescribed in U.S. patent application Ser. No. 60/237,639, the entirecontents of which are hereby incorporated by reference.

In another embodiment of the invention, the code symbology is atwo-dimensional code symbology and preferably it is a bar code and mostpreferably an n,k bar code, such as PDF417. In a further embodiment ofthe invention, auto-discrimination is added to the resulting code symbolto enable a reader to determine that the code symbol is an ink-spreadcompensated variant for the decoding thereof. In one embodiment, theauto-discrimination is added by using different data characters than inthe existing symbology. Alternatively, auto-discrimination comprisesusing a different subset of codewords than in the existing symbology. Inanother variation, auto-discrimination is added by using a unique datacharacter pattern to identify the code symbol as an ink-spreadcompensated variant. Further, auto-discrimination can be added byproviding a unique start pattern in the resulting code symbol, a uniquestop pattern in the resulting code symbol or both. Theauto-discrimination can also be added by providing a unique finderpattern in the resulting code symbol.

A method in accordance with the invention of decoding an ink-spreadcompensated variant of an existing n,k bar code symbology produced inaccordance with the invention comprises discriminating that the bar codesymbol is an ink-spread compensated variant and what the amount of theadded length, normalizing the width of a character to add the totaladded length and varying the threshold for the spaces to include thelength added thereto.

An ink-spread compensated n,k bar code symbology in accordance with theinvention comprises characters having k bars and k spaces of varyingwidth, wherein the width of each bar is from 1 to m modules in lengthand wherein the width of each space is from 1+x to m+x modules inlength, wherein 0<x≦2 modules in length, and wherein the overall lengthof each character is n+kx modules. Preferably, the n,k bar code is an11,3 bar code wherein the bars and spaces are from 1 to 4 modules inlength and most preferably x is 0.5 module or 1 module.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other features of the present invention will be morereadily apparent from the following detailed description and drawings ofillustrative embodiments of the invention in which:

FIG. 1 shows a n,k bar code called a Scanlet without ink-spreadcompensation intended to be used on different print media along withreferences to elements thereof;

FIG. 2A shows the bar code of FIG. 1;

FIG. 2B shows the bar code of FIG. 2A with ink-spread compensation inaccordance with the present invention;

FIG. 3A shows one character of a Scanlet in normal size;

FIG. 3B shows a gain compensated version of FIG. 3A;

FIG. 4 are the start pattern measurements for a Scanlet; and

FIG. 5 are character code measurements for a Scanlet.; and

FIG. 6 shows a schematic view of an exemplary optical code readingdevice having a decoder module in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, a bar code symbology is modified tocompensate for ink spreading by increasing the width of the spaceswithout decreasing the width of the printed lines. This new technique isthat it is inherently safer than conventional compensation techniqueswhen the amount of ink spread is unknown (e.g., when the same bar codeimage in a print ad goes to both newspapers and magazines, and will beprinted on a variety of paper substrates).

The technique of “Delta Distance Decoding” is sufficient to fullycompensate for variable amounts of ink spread, except for the fact thattoo much ink spread will cause the narrow spaces of the bar code tobecome so small as to negatively affect scanner performance. Traditionalpre-compensation techniques address this problem by reducing the size ofthe printed bars to thereby make the adjacent narrow spaces larger, atthe expense of the adjacent narrow bars, which can become smaller thannominal.

Use of the present invention raises two primary concerns. First, the newmethod makes the bar code somewhat larger (it grows by about 13% when“1.5 spaces” are used, and by about 27% when “2X spaces” are used).Second, unlike the traditional bar-shaving method, the present methodrequires that the decoder determine or auto-discriminate whether or nota given barcode has been pre-compensated in this new way. Given theseconcerns, the present method is most useful when the amount of inkspread is not known in advance.

Two methods for auto-discrimination are disclosed in detail below: (a)creating a variant of the symbology (e.g., changing the Stop pattern ofa code disclosed in the aforementioned pending application, hereinafterreferred to as a Scanlet, or using Code 128 with characters of theopposite bar parity), and (b) using only a subset of the encodablecharacter set for the first data character to “flag” the compensatedversion. For instance, if Code 128 characters are used, characterscontaining “T distances” that are all either 3X or 4X (beforepre-compensation) decode properly whether or not the decoder “thinks”that compensation is present.

To apply the new pre-compensation technique to any defined (n,k)character set, a new “stretched” version of the set is defined in whichthe bar widths are unchanged but all of the space widths of eachcharacter are increased by the same amount (typically either by 0.5X orby 1X). This creates a “new” bar/space character set that can betrivially mapped back to the original set by simply subtracting thatfixed amount from each measured T distance.

For example, Code 128 character set is a (11,3) code (each patterncomprises 11 modules, and contains 3 bars and 3 spaces) and is shownbelow as Table I. Applying the present methodology using 2X spaces tomaximize tolerance to ink spread produces a “stretched” (14,3) characterset. In this new set, each of the three spaces of each pattern have beenincreased by 1X, so a total of three modules have been added to eachpattern, but no 1X spaces have been used. The resulting set of patternscan be thought of as identical to the original Code 128 set, exceptthat:

-   -   Each set of 3 bars and 3 spaces must be normalized against 14        modules when decoding, rather than against 11, and    -   Each T distance that is calculated during the decode process        must be decreased by 1 before the pattern lookup occurs.

For example, as normally printed, the bars and spaces of the Code 128symbol character “00” have the series of widths 2,1,2,2,2,2 (in theorder bar, space, bar, space, bar, space). Summing each pair of adjacentelements, this forms a “T sequence” of 3,3,4,4,4. Applying the presentinvention using 2X minimum spacing produces a new width sequence of2,2,2,3,2,3 where the widths of the bars are unchanged, but the width ofeach space is increased by 1X. The new T sequence for this pattern is4,4,5,5,5, when normalized against 14 modules.

The normalization process starts by assuming that the overall characterwidth “p” (in this case the width of a set of 6 bars and spaces)represents a predetermined number of modules (11 for standard Code 128,but 14 for “2X-Stretched” Code 128). Then, each edge-to-similar-edgemeasurement is converted to an integer.

For example, assume that a laser spot traveled across this pattern at acertain rate so that crossing a 1-module bar took 100 microseconds, andcrossing a 2-module bar took 200 microseconds, and so on. The resultingmeasurements from crossing the “stretched” pattern (if no ink spreadoccurred) would be 200, 200, 200, 300, 200, and 300 microseconds. Thecharacter width is 1400 microseconds, the sum of these six measurements.

To calculate the T distances, the traversal rate for adjacent bars b andspaces s are summed, multiplied by the expected number of modules, anddivided by the total traversal time. In the present example, the first Tdistance is ((b1+s1) * 14)/p=((200+200) * 14)/1400=4. Continuing thesecalculations produces a T sequence for the stretched pattern of4,4,5,5,5. Subtracting 1 from each T distance re-creates the original“unstretched” sequence of 3,3,4,4,4. This sequence can then be decodedto find the intended value “00”.

As will be recognized, to arrive at the right calculations, the decoderneeds to know to normalize over 14 modules rather than 11. Surprisingly,in the particular case of (11,3) characters whose T distances are alleither 3 or 4, it turns out that the mathematical error introduced frommistakenly normalizing against 11 modules instead of 14 maps closely tothe correct value for the original “unstretched” character.

For example, for the first T distance of the “stretched” character, thecalculation becomes ((200+200) * 11)/1400=3.14 (very far from theprinted distance of 4, but very close to the “original” T of 3). Astretched T of 5 (that was originally a T of 4), when mis-normalizedagainst 11, comes even closer to the intended value. In this example,((200+300) * 11)/1400=3.93. This property can be useful as anauto-discrimination method (see below). More generally, the errorintroduced for T distances of 2, or for T distances larger than 4becomes significant and therefore, except for certain characterpatterns, it is important to normalize against the correct number ofmodules (in this example, 14 instead of 11).

It should also be noted that, if the printing process is generallyadequate in terms of well-placed edges, and ink-spread is the onlyproblem to be addressed, then this technique is advantageous, comparedto the alternative of simply printing the symbol at twice the Xdimension (which would also result in 2X as the minimum width, but forboth bars and spaces). Doubling the X dimension makes the symbolcharacter 100% larger, whereas “stretching” the spaces to 2X makes thesymbol character only (14/11) or 27% larger, yet still doubling thewidth of the narrow spaces for maximum ink spread tolerance.

Although patterns stretched by 1X have been discussed above, thepre-compensation technique can “stretch” each space by amounts otherthan 1X. Stretching by 0.5X, for example, results in a smaller sizepenalty (each character grows from 11X to 12.5X, rather than to 14X),while still providing ample tolerance for ink spread (50% ink spread, asubstantial amount, will merely reduce the 1.5X spaces back to their“original” 1X).

The new pre-compensation method of the current invention may be appliedto any binary or “edge to similar edge decodable” symbology (usuallycharacterized as an (n,k) symbology), either already in existence, or ina new symbology. To apply it to an existing symbology, however, someusage convention (within a closed system or other controlledapplication) or differentiating feature should be added to the symbologyto inform the decoder that wider spaces are being employed. A “usageconvention” technique will be described in the first preferredembodiment below. A “differentiating feature” technique for open systems(which could consist of a new Start and/or Stop pattern, or use of analternate parity subset of the same (n,k) patterns), will also bedescribed below.

The simplest form of usage convention would be a prior agreement toutilize only the print gain tolerant variant of a chosen symbology. Forexample, it could be agreed by the printing and scanning parties to aclosed-system application that Code 128 barcodes will always be printedusing 1.5X wide spaces.

A simple usage convention suffices for gain tolerant Binary codes,because a well-chosen combination of printing and decoding techniquescan allow standard and gain-tolerant Binary codes to be transparentlyintermixed in the same system. For example, the standard “Factor R” Code39 decode algorithm (as disclosed in the AIM symbology specification),if applied to Code 39 symbols printed at a 3:1 wide:narrow ratio, worksabout as well for symbols with 2X narrow spaces as for traditionalsymbols with 1X narrow spaces. Alternately, the convention could specifyan alternate decoding technique (which sets separate thresholds for barsand for spaces) which would work identically whether a 2:1 symbol (i.e.,using 1X and 2X bars) was printed using 1X and 2X spaces, 1.5X and 2.5Xspaces, or 2X and 3X spaces. As can be seen, the auto-discriminationissue is fairly easily solved for the case of Binary codes, and so theremainder of this discussion will focus on ways to auto-discriminategain-tolerant versions of (n,k) codes.

A more flexible scheme would utilize a data convention designed to allowboth standard Code 128 and print-gain-tolerant Code 128, for example, tocoexist in the same application. For example, it could be agreed by theprinting and scanning parties to a closed-system application, that Code128 barcodes starting with certain numbers were printed with standard 1Xnarrow spaces, whereas Code 128 bar codes starting with certain othernumbers were printed with 1.5X narrow spaces. In the case of Code 128,certain symbol character patterns, such as the one representing “02”,happen to use values of either 3 or 4 for all of theiredge-to-similar-edge measurements. As shown above for the case of 2Xminimum spaces, these values decode with very little error, when printedas a 12.5X character but mistakenly normalized against 11 modules. As anexample, for the first T distance of the 1.5X “stretched” character, the“mis-normalized” calculation becomes ((200+150) * 11)/1250=3.08 (veryfar from the printed distance of 3.5, but very close to the “original” Tof 3). A stretched T of 4.5 (that was originally a T of 4), whenmis-normalized against 11, comes even closer to the intended value. Inthis example, ((200+250) * 11)/1250=3.96.

Thus, these patterns (that originally contained only 3X and 4X Tdistances) could be used in the first data position (by convention) suchthat one subset of these patterns only appear in the 1.0X symbols, whilea second subset of them only appear in the 1.5X symbols. These patternswill decode correctly using an 11X width even if they are printed in astretched 14X format. The decoder could auto-discriminate the narrowspace width being used simply by decoding the first character (assuminga standard 11X character width) and checking which subset of thosereserved patterns it was.

The technique just disclosed, of reserving certain patterns to denotethe “wider” version of the characters, is simple to apply to an existingsymbology design, but it can be relatively inefficient because the firstdata character pattern no longer carries a full range of data. For a newsymbology design, a preferred autodiscrimination technique is to definevariations of the symbology's Start and/or Stop patterns and/ordata-character patterns, so that the decoder could ascertain the narrowspace width from the choice of patterns employed. If the recognition ofvariants is based on Start and/or Stop patterns (as opposed to usingalternative subsets of data-character patterns), it would further bedesirable to define these alternate sets of Start/Stop patterns in sucha way that a common “finder” routine could identify either version,without doubling the computation requirements of the “finder” process.Therefore, two additional preferred embodiments are disclosed below, oneusing an alternate set of data character patterns, and one usingalternate sets of Start and Stop patterns.

For each given n,k symbology used as a starting point for theapplication of the techniques described herein, there can be one or moredifferent preferred embodiments of this invention. This is because thedesign of variations of either the data characters, or of the Startand/or Stop characters, depends both on the standard patterns for eachsymbology, and on the other symbologies that will also be in use in agiven application. One n,k symbology shown in FIG. 1, called Scanlets,is a consumer-oriented bar code that is a particularly appropriatestarting point, because of the expectation that printed Scanlets will begenerated from an unusually large number of sources, with less controlover print gain than is typical for bar codes in industrialapplications.

Standard Scanlets use the standard (11,3,E) data characters of Code 128(eleven modules per character, consisting of 3 bars and 3 spaces, wherethe sum of the bars is always an Even number of modules). A second,print-gain-tolerant, version of Scanlets can be easily defined, by usingthe same Start and Stop patterns (except that the spaces are allincrementally wider than standard), but using data character patterns(and check character patterns) that are nominally (11,3) patterns, butwhere the Odd subset, rather than the Even subset, is used, such thatthe sum of the bars is always an odd number of modules, and where thespaces are all widened by a predetermined amount (for example, by 1X).Table II is an odd-parity character encodation that can be ink-spreadcompensated according to the present invention. For the odd-parityScanlets in Table II, only 103 values are needed and the others would beexcluded. (For example, values 0 and 101 would be excluded, because theybegin or end with four narrow elements in a row).

In this embodiment, the decoding process is quite similar to that forunmodified Scanlet decoding except that the character set table needs tolist the patterns for both the odd and even subsets of patterns. Sincethe Start and Stop patterns for standard Scanlets were defined tominimize symbol size, and since this embodiment uses the same patterns(widened only by the print-tolerant spaces), this approach creates aminimum-sized symbology variant. However, this embodiment does not allowthe decoder to pick between the two variants (for example, 1X spaces,vs. 1.5X spaces) based on the start and stop patterns alone. Therefore,it requires the decoder to try both decode approaches (i.e., assuming11X characters with 1X spaces and even parity, then assuming 12.5Xcharacters with 1.5X spaces and odd parity), until one assumptionresults in an invalid character. In the worst case (which would be veryrare, but not impossible), all characters will decode both ways, and thedecoder would need to choose the “best fit” one (i.e., the assumptionthat resulted in decode measurements that were closer to nominal).Various selection and best fit techniques known to those of skill in theart could be used for this purpose.

One preferred embodiment of how Scanlets could be adapted to use thepresent invention, using unique Start and unique Stop patterns, isdisclosed herein. Varying both patterns is preferred, as it provides aself-check that the correct version has been discriminated. In thisembodiment, a total of three variants of Scanlets, offering varyingdegrees of print gain tolerance, can be auto-discriminated. One of theseversions is a standard Scanlet which offers no extra degree of printgain tolerance. The two new versions, described herein, are called “GainTolerant” or GT Scanlets. These versions compensate for anticipatedprint gain by increasing the width of the spaces, without acorresponding decrease in the width of the bars. Therefore, thesegain-tolerant versions may be utilized when the same Scanlet image willbe printed to various press/substrate combinations, with varying orunknown amounts of ink spread. A single image may be safely used forprinting systems with variable amounts of print gain (or reduction),because the narrow bars need never be less than 1X wide. If even moregain tolerance is desired, traditional bar width reduction (shaving) canbe applied to a GT Scanlet image.

The GT versions of Scanlets use the same set of symbol characterpatterns as do standard Scanlets, except that the three spaces of eachpattern are each increased by 0.5X (in GT15 Scanlets) or by 1.0X (inGT20 Scanlets). The bars in all versions of Scanlets are either 1, 2, 3,or 4 modules wide. The spaces in GT15 Scanlets are 1.5, 2.5, 3.5, and4.5 modules wide, and the spaces in GT20 Scanlets are 2, 3, 4, and 5modules wide. Printing processes of any dot-pitch resolution may useGT20 Scanlets, whereas GT15 Scanlets are preferably not used with alow-resolution printing process (less than 5 dots per narrow bar) unlessan even number of dots per narrow bar is selected. GT15 and GT20Scanlets may be read by suitably programmed bar code decoders which havebeen designed to auto-discriminate them from each other, from standardScanlets, and from other symbologies.

Except for the differences described herein, the structure of all threeversions of Scanlets are as described in the aforementioned application.

-   -   a. All three versions of Scanlets preferably use the same        Interface Graphic, always printed at the dimensions of standard        Scanlets.    -   b. All three versions of Scanlets preferably use a Finder        pattern consisting of a series of four 1X bars interleaved with        four narrow spaces (but for GT15 and GT20 Scanlets, the narrow        spaces are 1.5X and 2X, respectively). The Interface Graphic is        identical for all three versions, and thus the first bar of the        Start pattern is always 2X wide. However, the first space of the        Start pattern (which is immediately to the left of the first bar        of the Finder pattern) is 3X for standard Scanlets, 2.5X for        GT15 Scanlets, and 4X for GT20 Scanlets. These patterns were        chosen so that one Finder algorithm works with all three        versions, while the full Start pattern provides a check that the        decode of the Stop pattern indicated the correct version.    -   c. All three versions of Scanlets preferably use the same set of        patterns for data and check characters, with the same values and        meanings as standard Scanlets. The only difference is that the        three spaces of each pattern are each enlarged (each by 0.5X or        1.0X, for GT15 Scanlets or GT20 Scanlets, respectively).    -   d. Standard Scanlets, GT15 Scanlets, and GT20 Scanlets        preferably have three distinct Stop patterns, with some features        in common. All begin with a bar/space sequence 1n1n2n, where ‘n’        represents a narrow space (1, 1.5, or 2X wide, respectively),        and all have a total of 8 bars and spaces, followed by a        terminating bar (that may be any width from one to four modules        wide). Thus, in all cases, the width of the first six elements        of the Stop pattern is less than 75% of the width of the        preceding data character. This change in element density is        utilized to recognize the Stop pattern. The fourth bar and        fourth space of the Stop pattern are (1,1), (4, 1.5), and (2,5)        for standard Scanlets, GT15 Scanlets, and GT20 Scanlets,        respectively. These patterns were chosen so that a single        one-module edge error cannot map to another valid pattern, and        so that the versions can be auto-discriminated before the number        of space modules per character is known.

The following presents a specific decode algorithm that canauto-discriminate properly between all three versions of Scanlets, whileusing a common “finding” algorithm in order to minimize the processingrequirements (presenting the forward-scan logic only, for simplicity):

-   1. Find a bar element that is larger than each of the next four    bars. To minimize the chance of accidentally accepting a pattern    that includes bars that are not in fact nominally smaller than the    first one (but are slightly smaller, due to random print defects or    scanner noise) reduce the candidate “larger” bar by {fraction    (1/16)} before doing the four comparisons.-   2. Check that the first interleaved space is larger than each of the    next four spaces; reduce the candidate “larger” space by {fraction    (1/16)} before doing the four comparisons.-   3. Verify that the sum of these supposed 8 narrow elements is less    than the sum of the next six elements (which should be the first    data character), but greater than one-half of that 6-element sum.-   4. Verify that for each of the seven T distances of the Finder (not    including the two leading elements of the complete Start pattern),    each T normalizes to 2 modules when a total of 8 modules is assumed.    This works regardless of whether the interleaved spaces are 1X,    1.5X, or 2X wide.-   5. Do not decode the two leading T distances of the Start pattern    until after the Stop pattern has been verified and decoded. The Stop    pattern will tell the decoder which version of Scanlets has been    printed, and then these leading T's of the Start pattern can be    decoded. This serves as a check that the correct version was    identified from the Stop pattern: the leading T's of the Starts have    been selected such that, if the wrong version is assumed from a    misdecoded Stop, the decode of the Start will not match the expected    result.-   6. Find the Stop pattern, using the same technique as described for    a standard Scanlet (the first six elements of the new Stop patterns    still maintain the property that they are less than ¾ the width of a    data character). Decode the Stop pattern using the following    substeps, to determine which version of Scanlets has been printed.    -   a) Compare the sum of the six elements just found, to T7, the        sum of the next two elements.        -   i) If (2* T7) is less than the width of the sum of the            previous six elements, then this 8-element Stop pattern            indicates a standard Scanlet. Calculate Z based on the first            six elements, normalized to 7 modules. Verify that the eight            elements decode as a T sequence of 2, 2,2, 3, 3, 2,2.        -   ii) Otherwise (i.e., (2 * T7) is greater than or equal to            the width of the sum of the previous six elements):            -   (a) if the fourth bar (element seven) is greater than                the fourth space (element eight), this indicates a GT15                Scanlet. Calculate Z based on the first six elements,                normalized to 8.5 modules. Verify that the eight                elements decode as a T sequence of 2.5, 2.5, 2.5, 3.5,                3.5, 5.5, 5.5.            -   (b) Otherwise, this indicates a GT20 Scanlet. Calculate                Z based on the first six elements, normalized to 10                modules. Verify that the eight elements decode as a T                sequence of 3, 3, 3, 4, 4, 4, 7.    -   b) Now that the Scanlet version has been determined, and        therefore the size of the narrow spaces is known, the leading        elements of the Start pattern can be verified. Calculate the        value of Z as:        Z=(f1+f3+f5+f7)/nModules,    -    Where nModules is 8, 10, or 12, for standard Scanlets, GT15        Scanlets, or GT20 Scanlets, respectively.    -   Verify that the two measurements (T1, T2) decode to (5, 4) if        decoding a standard Scanlet, (4.5, 3.5) if decoding a GT15        Scanlet, or (6, 5) if decoding a GT20 Scanlet. In all cases,        each measurement is given a tolerance of +/−0.5Z.-   7. Complete the decode of the Start pattern, which serves as a check    that the correct version has been discriminated.-   8. Complete the decode of the symbol as described for standard    Scanlets in the attached specification, except that the character    decode now takes into account which version is being scanned (see    the Character-Decode Algorithm below). The character set tables do    not need to change, nor does the bar-parity table (the bar-parity    check changes, in that normalization is against 11, 12.5, or 14    modules, depending on version). Also, to maximize ink-spread    tolerance (since these wider-space Scanlets can easily tolerate 100%    ink spread), the decoder should do an ink-spread correction on each    data character, just before doing its bar parity check. The ink    spread of the Start patterns' elements is easily calculated (once it    has been determined whether the Scanlet has nominal 1X, 1.5X, or 2X    spaces). This initial value would be used to correct the first data    character; the first data character's ink spread can then be    calculated and applied to the second character, and so forth. To    reduce computation time on unsuccessful scans, the entire process of    verifying bar parity could be deferred until after the entire    Scanlet has been processed, and its check character has been    validated.    Character-Decode Algorithm

The number of modules per symbol character, n, is 11 for standardScanlets, 12.5 for GT15 Scanlets, and 14 for GT20 Scanlets. Thefollowing steps can be used to decode each (11,3) character within aScanlet:

-   1. Calculate eight width measurements p, e₁, e₂, e₃, e₄, b₁, b₂, and    b₃ (see FIG. 4).-   2. Convert measurements e₁, e₂, e₃, and e₄ to normalized values E₁,    E₂, E₃, and E₄ which will represent the module width (E_(i)) of    these measurements. The following method is used for the i-th value.

For standard Scanlets and GT20 Scanlets:

-   -   If 1.5 p/n≦e_(i)<2.5 p/n, then E_(i)=2 for a standard Scanlet,        otherwise the character is in error.    -   If 2.5 p/n≦e_(i)<3.5 p/n, then E_(i)=3    -   If 3.5 p/n≦e_(i)<4.5 p/n, then E_(i)=4    -   If 4.5 p/n≦e_(i)<5.5 p/n, then E_(i)=5    -   If 5.5 p/n≦e_(i)<6.5 p/n, then E_(i)=6    -   If 6.5 p/n≦e_(i)<7.5 p/n, then E_(i)=7    -   If 7.5 p/n≦e_(i)<8.5 p/n, then E_(i)=8 for a GT20 Scanlet,        otherwise the character is in error.

Otherwise the character is in error.

For GT15 Scanlets only:

-   -   If 1.9 p/n≦e_(i)<3 p/n, then E_(i)=2    -   If 3 p/n≦e_(i)<4 p/n, then E_(i)=3    -   If 4 p/n≦e_(i)<5 p/n, then E_(i)=4    -   If 5 p/n≦e_(i)<6 p/n, then E_(i)=5    -   If 6 p/n≦e_(i)<7 p/n, then E_(i)=6    -   If 7 p/n≦e_(i)<8.15 p/n, then E_(i)=7

Otherwise the character is in error.

Note that the lower bound for a normalized value of 2, and the upperbound for a normalized value of 7, allow for a small amount of round-offerror that can be introduced when a GT Scanlet's X dimension translatesto an odd number of printer dots per nominal module.

-   3. If decoding a GT20 Scanlet, subtract 1 from each of the E_(n)    values calculated above. Look up the character in a decode table    using the four values E₁, E₂, E₃, and E₄ as the key. This decode    table may be found in the Code 128 specification, or may be derived    directly from Table 1. If using the decode table in the Code 128    specification, note that the STOP_(A) and STOP_(B) patterns are    invalid when decoding a Scanlet.-   4. Retrieve character self-checking value V which is stored in the    table with the character (or which can be derived directly from    Table 1). The value V is equal to the sum of the modules for the    bars as defined for that character.-   5. Verify that (V−1.75)p/n<(b1+b2+b3)<(V+1.75)p/n

Otherwise the character is in error.

The calculation indirectly uses character parity to detect all decodeerrors caused by single non-systematic one-module edge errors.

In the embodiment where only two Scanlet versions are used, the standardScanlets utilize a subset of the bar and space patterns exactly asdefined in the Code 128 specification (although the values assigned tothose patterns are different). For improved immunity to excessive printgain, the gain-tolerant variation called GT Scanlets are preferred forScanlets printed at high densities (an X dimension of 10 mils or below).Although the overall structure is the same, 0.5X is added to the widthof each interior space of a GT Scanlet (when encoding, this 0.5X ispreferably rounded down to the nearest integer number of printer dots).

A GT Scanlet is shown in FIG. 2B, encoding the same data as FIG. 2A, atthe same X dimension. FIG. 3A illustrates the encodation of the pair ofdigits “34” in a standard Scanlet using symbol character 35. FIG. 3Bshows the same data encoded in a GT Scanlet. The bars are exactly asshown in FIG. 3A but each space is 0.5X wider than the FIG. 3Aencodation.

The Stop pattern of a standard Scanlet, such as shown in FIG. 1, haseight alternating dark and light elements, starting with a bar. Themodule widths of the Stop pattern elements form the sequence 1, 1, 1, 1,2, 1, 1, 1. These are followed by a terminating bar or other darkgraphical element, between one and four modules wide, whose function isto delineate the one-module width of the last space of the Stop pattern.

In one embodiment of the invention, the Stop pattern of a GT Scanlet haseight alternating dark and light elements, starting with a bar. Themodule widths of the Stop pattern elements form the sequence 1, 1.5, 1,1.5, 2, 1.5, 4, 1.5. These are followed by a terminating bar or otherdark graphical element, between one and four modules wide, whosefunction is to delineate the one-module width of the last space of theStop pattern.

With reference to the scanlet shown in FIG. 1, the Interface Graphicpattern at the left end of a Scanlet has two adjacent dark triangles,bordered by a reverse ‘L’ which extends 1X above and 1X below the barsof the body of the Scanlet. The bottom edge of the reverse ‘L’ isnominally 1X high and 13X wide, but is tapered at both ends as shown inFIG. 1. The right edge of the reverse ‘L’ is 2X wide throughout thecentral 10X of its height, but is tapered at the top and bottom. In theScanlet of FIG. 1, the triangles are each 4X wide, nominally 6X high(but this is not a critical dimension), and are positioned vertically tobe centered within the height of the bars of the body of the Scanlet.The rightmost triangle ends 2X to the left of the 2X vertical portion ofthe reverse ‘L’. The same Interface Graphic can be printed for bothstandard and GT Scanlets.

With regard to decoding, a standard Scanlet and a GT Scanlet can beauto-discriminated and decoded as follows. A candidate Scanlet can befound within a scan line of bar and space measured values, by using thefollowing steps (see FIG. 4 for a representation of the measurementsneeded to find and validate a Start pattern):

-   1. To find a Scanlet, perform the following steps at each bar    position:    -   a) sum the widths of the 8 elements starting from the current        bar position. Check that the sum of the next 6 elements is        greater than the sum of these 8, but less than 1.5 times the sum        of these 8. If so, then divide this sum of eight elements by 8        to obtain “Z”, the average module width. Validate these as a        candidate Finder pattern with seven edge-to-similar-edge        distances between 1.5Z and 2.5Z. For the Scanlet Finder pattern        shown in FIG. 4, this step consists of computing        Z=(f1+f3+f5+f7)/8 and checking that f1 through f7 are each        between 1.5Z and 2.5Z    -   b) To look also for a possible reverse scan, sum the current bar        width and the prior seven element widths. Check that the sum of        the 6 elements prior to these 8 is greater than the sum of these        8, but less than 1.5 times the sum of these 8. If so, divide by        sum of the 8 elements by 8 to obtain “Z”, the average module        width. Check for a trailing Finder pattern with seven        edge-to-similar-edge distances between 1.5Z and 2.5Z.    -   c) The leading elements of the Start pattern are not checked        until after the Stop pattern has been found and decoded (see        step 2).-   2. Verify that a valid Stop pattern was scanned, starting n elements    past the Finder pattern (if enough elements are present in that    direction), and starting n elements before the Finder pattern (if    enough elements are present in that direction), where n is an even    multiple of six, in the range of 18 to 48 inclusive. Search by    summing each set of six elements until a set is reached that, when    multiplied by 1.25, is less than the width of the previous group.    Then determine which version of Scanlets is present, and decode the    stop character accordingly, as follows:    -   a) Compare the third and fourth bars of the Stop pattern.        -   i) If the third bar is wider than the fourth bar, then this            8-element Stop pattern indicates a standard Scanlet.            Calculate Z based on these eight elements, normalized to 9            modules. Verify that the eight elements decode as a T            sequence of 2, 2, 2, 3, 3, 2, 2. Also verify that the total            width of these 8 elements is less than the total width of            the previous six elements, but greater than 0.75 times the            total width of the previous six elements.        -   ii) Otherwise (i.e., the fourth bar is wider than the third            bar), this indicates a GT Scanlet. Calculate Z based on the            first eight elements, normalized to 14 modules. Verify that            the eight elements decode as a T sequence of 2.5, 2.5, 2.5,            3.5, 3.5, 5.5, 5.5. Also verify that the total width of            these 8 elements is greater than the total width of the            previous six elements, but less than 1.25 times the total            width of the previous eight elements.    -   b) Now that the Scanlet version has been determined, and        therefore the size of the narrow spaces is known, the leading        elements of the Start pattern can be verified. Calculate the        value of Z as:        Z=(f1+f3+f5+f7)/nModules,    -    Where nModules is 8 or 10, for standard Scanlets or GT        Scanlets, respectively. Verify that the first two measurements        of the Start pattern (T1, T2) decode to (5, 4) if decoding a        standard Scanlet, or to (4.5, 3.5) if decoding a GT15 Scanlet.        In either case, each measurement is given a tolerance of        +/−0.5Z. Set the scan direction based on the validated Start and        Stop patterns.-   3. Beginning at the inner end of the Finder pattern, decode the    succeeding groups of six elements as standard Code 128 symbol    characters in the direction determined from step 3. Continue until    either an invalid data character pattern is detected, or until the    position of the Stop pattern has been reached. If a group of six    elements is of the proper width for a data character, but decodes to    a Code 128 value of 33, 62, or 92, the character is invalid. Unless    in the check character position, values greater than 102 are also    invalid.-   4. Verify that the symbol check character calculated is correct. In    addition, verify that the symbol contained at least three symbol    characters (including the check character, but excluding the Start    and Stop patterns) and at most eight symbol characters.-   5. Translate the symbol characters into a string of digits. Each    symbol character translates directly into a pair of digits (from the    “Scanlet Value” column of Table 1), in the range of “00” through    “99”.-   6. In addition, perform such other secondary checks on quiet zones,    beam acceleration, absolute timing, dimensions, etc., as are deemed    prudent and appropriate considering the specific reading device and    intended application environment.    In this algorithm the symbol is decoded using “edge to similar edge”    measurements, plus an additional measurement of the sum of the three    bar widths to check the parity of each symbol character.

The number of modules per symbol character, n, is 11 for standardScanlets, and 12.5 for GT Scanlets. Use the following steps to decodeeach character within a Scanlet:

-   1. Calculate eight width measurements p, e₁, e₂, e₃, e₄, b₁, b₂, and    b₃ (see FIG. 5).-   2. Convert measurements e₁, e₂, e₃, and e₄ to normalized values E₁,    E₂, E₃, and E₄ which will represent the module width (E_(i)) of    these measurements. The following method is used for the i-th value.

For standard Scanlets:

-   -   If 1.5 p/n≦e_(i)<2.5 p/n, then E_(i)=2    -   If 2.5 p/n≦e_(i)<3.5 p/n, then E_(i)=3    -   If 3.5 p/n≦e_(i)<4.5 p/n, then E_(i)=4    -   If 4.5 p/n≦e_(i)<5.5 p/n, then E_(i)=5    -   If 5.5 p/n≦e_(i)<6.5 p/n, then E_(i)=6    -   If 6.5 p/n≦e_(i)<7.5 p/n, then E_(i)=7

Otherwise the character is in error.

For GT Scanlets:

-   -   If 1.9 p/n≦e_(i)<3 p/n, then E_(i)=2    -   If 3 p/n≦e_(i)<4 p/n, then E_(i)=3    -   If 4 p/n≦e_(i)<5 p/n, then E_(i)=4    -   If 5 p/n≦e_(i)<6 p/n, then E_(i)=5    -   If 6 p/n≦e_(i)<7 p/n, then E_(i)=6    -   If 7 p/n≦e_(i)<8.15 p/n, then E_(i)=7

Otherwise the character is in error.

Note that the lower bound for a normalized value of 2, and the upperbound for a normalized value of 7, allow for a small amount of round-offerror that can be introduced when a GT Scanlet's X dimension translatesto an odd number of printer dots per nominal module.

-   3. Look up the character in a decode table using the four values E₁,    E₂, E₃, and E₄ as the key. This decode table may be found in the    Code 128 specification, or may be derived directly from Table I. If    using the decode table in the Code 128 specification, note that the    STOP_(A) and STOP_(B) patterns are invalid when decoding a Scanlet.-   4. Retrieve character self-checking value V which is stored in the    table with the character (or which can be derived directly from    Table I). The value V is equal to the sum of the modules for the    bars as defined for that character.-   5. Verify that (V−1.75)p/n<(b1+b2+b3)<(V+1.75)p/n. Otherwise the    character is in error.

The calculation indirectly uses character parity to detect all decodeerrors caused by single non-systematic one-module edge errors.

The Start pattern of a standard Scanlet has five bars and five spacescomprising 13 modules. The Stop pattern has four bars and four spacescomprising nine modules, terminated by a dark element at least onemodule wide. The decodability of the Start and Stop patterns can bemeasured using the standard verification formula for V used above, butsubstituting n=13 or n=9, rather than n=11, to reflect the lengths ofthose patterns.

The Start pattern of a GT Scanlet has five bars and five spacescomprising 14.5 modules. The Stop pattern has four bars and four spacescomprising fourteen modules, terminated by a dark element at least onemodule wide. The decodability of the Start and Stop patterns can bemeasured using the standard formula based on V and used above, butsubstituting n=14.5 or n=14, rather than n=12.5, to reflect the lengthsof those patterns.

The seven edge-to-similar-edge distances in the Finder patternpreferably are each 2.0+/−0.315Z, the measurement labeled t1 in FIG. 4preferably is 5.0+/−0.315Z, and the measurement labeled t2 in FIG. 4preferably is 4.0+/−0.315Z. For these measurements, Z is the averagemeasured module width over the eight modules of the Finder Pattern.

The width of the terminating dark element to the right of the Stoppattern preferably is at least 1X wide, but no more than 4X wide. Anextra edge-to-similar-edge measurement T, summing the last space of theStop pattern and the terminating dark element, can be made on each scanreflectance profile. Using the value of Z from the Stop pattern, eachscan reflectance profile under ISO/IEC 15416 preferably can be measuredand graded as follows:T>=1.685Z and T<=5.75Z: Grade 4T<1.685Z or T>5.75Z: Grade 0

FIG. 6 shows a reading device 10 for reading optical codes. The readingdevice has a decoder module 12, i.e., a decoder, for performing analgorithm for decoding scanned optical codes.

As is well known in the art, graphics software used to create bar codeson pixel-based printers must scale each bar and space exactly to thepixel pitch of the printer or digital imaging system being used. Foredge to similar edge decodable symbologies, like Scanlets, the number ofpixels comprising each symbol character must be a fixed and constantinteger multiple of the number of modules in the symbol character. ForScanlets, the number of modules is 11 for symbol character values 0 to105. Therefore, a given printer can only print a certain set of Xdimensions.

Compensation for uniform bar width growth (or loss) should be in equaloffsetting amounts on all bars and spaces in the symbol. This can beaccomplished by changing an integer number of pixels from dark to lightor light to dark in the same manner for each bar-space pair in thesymbol. For example, a vertical column of pixels along the same edge(leading or trailing) of every bar in the symbol could be changed fromdark to light. Alternatively, pixels along both edges of every bar inthe symbol could be changed from dark to light, provided that theprinter resolution is sufficient to allow this to be performeduniformly. Any set of dark to light or light to dark pixel changes isacceptable provided the adjustment is performed consistently across thewhole symbol and does not change the edge to similar edge measurementsor the total symbol character width. Failure to follow these principlescan result in degraded symbol quality and unreadable symbols.

General-purpose printing software designed to support a wide range ofprinters can be used to provide a user with the capability of adjustingthe X dimension and bar width growth or loss.

(a) Programmer's Example

The principles discussed above can be reduced to the following set ofrules useful for digital bar code design files:

-   1. Convert the desired X dimension to a module size in pixels,    rounded down to the nearest integer (or rounded up, if rounding down    would cause the X dimension to fall below the minimum for this    application).-   2. Determine the number of pixels corresponding to the desired    compensation for uniform bar width growth, and round up to the next    larger integer (or round down, if rounding up would cause the pixels    per dark module to fall below one-half the nominal number of pixels    per modules determined above). If compensation for bar width    reduction, rather than bar width growth, is needed, perform the    equivalent rounding (that is, round up, unless rounding up would    cause the pixels per light module to fall below one-half of    nominal).-   3. Apply the above results to determine the pixel count of every bar    and space in the symbol.

EXAMPLE

Using a printing device that has 24 dots per mm, a digital bar codedesign file is created for a 0.27 mm X dimension symbol with 0.06 mm ofbar width reduction.

-   -   The module size is 24 dots/mm×0.27 nm/module=6.5 pixels, which        rounds down to 6 pixels per module.    -   The desired bar growth compensation is 0.06 mm×24 pixels/mm=1.4        pixels, which rounds up to 2 pixels.

This process results in the following pixel count for bars and spaces asillustrated in Table V.

As noted above, one should also consider how a 1.5X spacing will beaffected by printing on a printer where the number of dots for a singlemodule width is an odd number. The decision by the software for printingthe bar code would be whether to round up or round down. Tables III andIV illustrate the errors that are introduced by rounding down androunding up respectively. Rounding the fractional spaces down byone-half dot, rather than up, is advantageous, as can be seen bycomparing Table III with Table IV. Table III shows that rounding downcauses the inherent decoding error for the smallest and largest Tdistances to move the decision points away from the nearest validneighboring T choices. In contrast, rounding up (shown in Table IV)causes these “outermost” decision points to move closer to the nearestvalid neighboring choices, which increases the probability that anyadditional printing imperfections, added to this inherent inaccuracy,will cause the decode process to fail. The decode algorithms disclosedherein take advantage of this round-off-error “directionality” whensetting the thresholds for the largest and smallest T distances.

It will be understood that the embodiments described hereinabove aremerely illustrative and are not intended to limit the scope of theinvention. It is realized that various changes, alterations,rearrangements and modifications can be made by those skilled in the artwithout substantially departing from the spirit and scope of the presentinvention.

TABLE I C128 Scanlet Value Value B S B S B S 00 00 2 1 2 2 2 2 01 01 2 22 1 2 2 02 02 2 2 2 2 2 1 03 03 1 2 1 2 2 3 04 04 1 2 1 3 2 2 05 05 1 31 2 2 2 06 06 1 2 2 2 1 3 07 07 1 2 2 3 1 2 08 08 1 3 2 2 1 2 09 09 2 21 2 1 3 10 10 2 2 1 3 1 2 11 11 2 3 1 2 1 2 12 12 1 1 2 2 3 2 13 13 1 22 1 3 2 14 14 1 2 2 2 3 1 15 15 1 1 3 2 2 2 16 16 1 2 3 1 2 2 17 17 1 23 2 2 1 18 18 2 2 3 2 1 1 19 19 2 2 1 1 3 2 20 20 2 2 1 2 3 1 21 21 2 13 2 1 2 22 22 2 2 3 1 1 2 23 23 3 1 2 1 3 1 24 24 3 1 1 2 2 2 25 25 3 21 1 2 2 26 26 3 2 1 2 2 1 27 27 3 1 2 2 1 2 28 28 3 2 2 1 1 2 29 29 3 22 2 1 1 30 30 2 1 2 1 2 3 31 31 2 1 2 3 2 1 32 32 2 3 2 1 2 1 33 N/A 1 11 3 2 3 34 33 1 3 1 1 2 3 35 34 1 3 1 3 2 1 36 35 1 1 2 3 1 3 37 36 1 32 1 1 3 38 37 1 3 2 3 1 1 39 38 2 1 1 3 1 3 40 39 2 3 1 1 1 3 41 40 2 31 3 1 1 42 41 1 1 2 1 3 3 43 42 1 1 2 3 3 1 44 43 1 3 2 1 3 1 45 44 1 13 1 2 3 46 45 1 1 3 3 2 1 47 46 1 3 3 1 2 1 48 47 3 1 3 1 2 1 49 48 2 11 3 3 1 50 49 2 3 1 1 3 1 51 50 2 1 3 1 1 3 52 51 2 1 3 3 1 1 53 52 2 13 1 3 1 54 53 3 1 1 1 2 3 55 54 3 1 1 3 2 1 56 55 3 3 1 1 2 1 57 56 3 12 1 1 3 58 57 3 1 2 3 1 1 59 58 3 3 2 1 1 1 60 59 3 1 4 1 1 1 61 60 2 21 4 1 1 62 N/A 4 3 1 1 1 1 63 61 1 1 1 2 2 4 64 62 1 1 1 4 2 2 65 63 1 21 1 2 4 66 64 1 2 1 4 2 1 67 65 1 4 1 1 2 2 68 66 1 4 1 2 2 1 69 67 1 12 2 1 4 70 68 1 1 2 4 1 2 71 69 1 2 2 1 1 4 72 70 1 2 2 4 1 1 73 71 1 42 1 1 2 74 72 1 4 2 2 1 1 75 73 2 4 1 2 1 1 76 74 2 2 1 1 1 4 77 75 4 13 1 1 1 78 76 2 4 1 1 1 2 79 77 1 3 4 1 1 1 80 78 1 1 1 2 4 2 81 79 1 21 1 4 2 82 80 1 2 1 2 4 1 83 81 1 1 4 2 1 2 84 82 1 2 4 1 1 2 85 83 1 24 2 1 1 86 84 4 1 1 2 1 2 87 85 4 2 1 1 1 2 88 86 4 2 1 2 1 1 89 87 2 12 1 4 1 90 88 2 1 4 1 2 1 91 89 4 1 2 1 2 1 92 N/A 1 1 1 1 4 3 93 90 1 11 3 4 1 94 91 1 3 1 1 4 1 95 92 1 1 4 1 1 3 96 93 1 1 4 3 1 1 97 94 4 11 1 1 3 98 95 4 1 1 3 1 1 99 96 1 1 3 1 4 1 100  97 1 1 4 1 3 1 101  983 1 1 1 4 1 102  99 4 1 1 1 3 1 103  (100)  2 1 1 4 1 2 104  (101)  2 11 2 1 4 105  (102)  2 1 1 2 3 2

TABLE II Pattern: T-Distances: bsbsbs val = 0: 111134 T: 22247 val = 1:111233 T: 22356 val = 2: 111314 T: 22445 val = 3: 111332 T: 22465 val =4: 111413 T: 22554 val = 5: 111431 T: 22574 val = 6: 112124 T: 23336 val= 7: 112142 T: 23356 val = 8: 112223 T: 23445 val = 9: 112241 T: 23465val = 10: 112322 T: 23554 val = 11: 112421 T: 23663 val = 12: 113114 T:24425 val = 13: 113132 T: 24445 val = 14: 113213 T: 24534 val = 15:113231 T: 24554 val = 16: 113312 T: 24643 val = 17: 113411 T: 24752 val= 18: 114122 T: 25534 val = 19: 114221 T: 25643 val = 20: 121133 T:33246 val = 21: 121214 T: 33335 val = 22: 121232 T: 33355 val = 23:121313 T: 33444 val = 24: 121331 T: 33464 val = 25: 121412 T: 33553 val= 26: 122123 T: 34335 val = 27: 122141 T: 34355 val = 28: 122222 T:34444 val = 29: 122321 T: 34553 val = 30: 123113 T: 35424 val = 31:123131 T: 35444 val = 32: 123212 T: 35533 val = 33: 123311 T: 35642 val= 34: 124121 T: 36533 val = 35: 131114 T: 44225 val = 36: 131132 T:44245 val = 37: 131213 T:44334 val = 38: 131231 T: 44354 val = 39:131312 T: 44443 val = 40: 131411 T:44552 val = 41: 132122 T: 45334 val =42: 132221 T: 45443 val = 43: 133112 T:46423 val = 44: 133211 T: 46532val = 45: 141113 T: 55224 val = 46: 141131 T:55244 val = 47: 141212 T:55333 val = 48: 141311 T: 55442 val = 49: 142121 T:56333 val = 50:143111 T: 57422 val = 51: 211124 T: 32236 val = 52: 211142 T:32256 val =53: 211223 T: 32345 val = 54: 211241 T: 32365 val = 55: 211322 T:32454val = 56: 211421 T: 32563 val = 57: 212114 T: 33325 val = 58: 212132 T:33345 val = 59: 212213 T: 33434 val = 60: 212231 T: 33454 val = 61:212312 T: 33543 val = 62: 212411 T: 33652 val = 63: 213122 T: 34434 val= 64: 213221 T: 34543 val = 65: 214112 T: 35523 val = 66: 214211 T:35632 val = 67: 221123 T: 43235 val = 68: 221141 T: 43255 val = 69:221222 T: 43344 val = 70: 221321 T: 43453 val = 71: 222113 T: 44324 val= 72: 222131 T: 44344 val = 73: 222212 T: 44433 val = 74: 222311 T:44542 val = 75: 223121 T: 45433 val = 76: 224111 T: 46522 val = 77:231122 T: 54234 val = 78: 231221 T: 54343 val = 79: 232112 T: 55323 val= 80: 232211 T: 55432 val = 81: 241121 T: 65233 val = 82: 242111 T:66322 val = 83: 311114 T: 42225 val = 84: 311132 T: 42245 val = 85:311213 T: 42334 val = 86: 311231 T: 42354 val = 87: 311312 T: 42443 val= 88: 311411 T: 42552 val = 89: 312122 T: 43334 val = 90: 312221 T:43443 val = 91: 313112 T: 44423 val = 92: 313211 T: 44532 val = 93:321113 T: 53224 val = 94: 321131 T: 53244 val = 95: 321212 T: 53333 val= 96: 321311 T: 53442 val = 97: 322121 T: 54333 val = 98: 323111 T:55422 val = 99: 331112 T: 64223 val = 100: 331211 T: 64332 val = 101:341111 T: 75222 val = 102: 411122 T: 52234 val = 103: 411221 T: 52343val = 104: 412112 T: 53323 val = 105: 412211 T: 53432 val = 106: 421121T: 63233 val = 107: 422111 T: 64322

TABLE III Rounding error for GT15, for odd numbers of dots per bar: nBar3 5 7 9 11 13 SpaceAdd 1 2 3 4 5 6 T: 2 2.431 2.459 2.471 2.477 2.4822.484 3 3.472 3.484 3.488 3.491 3.493 3.494 4 4.514 4.508 4.506 4.5054.504 4.503 5 5.556 5.533 5.523 5.518 5.515 5.512 6 6.597 6.557 6.5416.532 6.526 6.522 7 7.639 7.582 7.558 7.545 7.537 7.531 error: T2:−0.069 −0.041 −0.029 −0.023 −0.018 −0.016 T3: −0.028 −0.016 −0.012−0.009 −0.007 −0.006 T4: 0.014 0.008 0.006 0.005 0.004 0.003 T5: 0.0560.033 0.023 0.018 0.015 0.012 T6: 0.097 0.057 0.041 0.032 0.026 0.022T7: 0.139 0.082 0.058 0.045 0.037 0.031

TABLE IV Rounding error for GT15, for odd numbers of dots per bar: nBar3 5 7 9 11 13 SpaceAdd 2 3 4 5 6 7 T: 2 2.564 2.539 2.528 2.522 2.5182.515 3 3.526 3.516 3.511 3.509 3.507 3.506 4 4.487 4.492 4.494 4.4964.496 4.497 5 5.449 5.469 5.478 5.482 5.486 5.488 6 6.410 6.445 6.4616.469 6.475 6.479 7 7.372 7.422 7.444 7.456 7.464 7.470 error: T2: 0.0640.039 0.028 0.022 0.018 0.015 T3: 0.026 0.016 0.011 0.009 0.007 0.006T4: −0.013 −0.008 −0.006 −0.004 −0.004 −0.003 T5: −0.051 −0.031 −0.022−0.018 −0.014 −0.012 T6: −0.090 −0.055 −0.039 −0.031 −0.025 −0.021 T7:−0.128 −0.078 −0.056 −0.044 −0.036 −0.030

TABLE V Correcting pixels for imaging resolution and bar width reductionPixel Count Module Count Bars Spaces 1 4 8 2 10 14 3 16 20 4 22 26

1. An optical code reading device for reading presented compensatedoptical codes having printed areas and spaces, the reading devicecomprising: a decoder module for decoding a presented compensatedoptical code, wherein the decoder module includes software instructionsexecutable on a processor for performing an algorithm including thesteps of: uncompensating the compensated optical code by compensatingfor a predetermined adjustment in length of a dimension of individualspaces of the optical code without compensating for a change in thelength of the dimension of individual printed areas of the compensatedoptical code for generating an uncompensated optical code; and decodingthe uncompensated optical code.
 2. The device according to claim 1,wherein the uncompensating step includes the step of normalizing thecompensated optical code in accordance with a sum of the length of thedimension of the printed areas and spaces of the compensated opticalcode.
 3. The device according to claim 1, wherein the normalizing stepincludes the steps of: determining an edge to similar edge distance forrespective adjacent printed areas and spaces of the compensated opticalcode; and normalizing the respective determined edge to similar edgedistances for generating the uncompensated optical code.
 4. The deviceaccording to claim 1, wherein the decoding the uncompensated code stepincludes the steps of: performing a look-up operation in a table storedin a database that is accessible by the decoder module by looking up theuncompensated optical code; and retrieving a corresponding decoded code.5. The device according to claim 1, wherein the algorithm furthercomprises the step of determining the value of the predetermined changefrom at least a portion of the compensated optical code.
 6. The deviceaccording to claim 1, wherein the optical code reading device is a laserscanning device.
 7. The device according to claim 1, wherein the opticalcode is encoded by a bar code encodation scheme.
 8. The device accordingto claim 1, wherein the optical code is encoded by an n,k bar codeencodation scheme, wherein the predetermined length is a function of amodule width of a symbol for a bar code of the compensated optical code.9. The device according to claim 8, wherein the predetermined length isx modules, 0<x≦2.
 10. The device according to claim 1, wherein theoptical code is encoded by a two-dimensional encodation scheme.
 11. Thedevice according to claim 1, wherein the algorithm further includes thestep of automatically discriminating a presented compensated opticalcode from a presented uncompensated optical code.
 12. The deviceaccording to claim 11, wherein the discriminating step is performed on apresented compensated optical code without uncompensating thecompensated optical code.
 13. The device according to claim 11, whereinthe discriminating step includes the step of recognizing a pattern of atleast a portion of the bars and spaces which indicates that thepresented optical code is a compensated optical code.
 14. The deviceaccording to claim 13, wherein the pattern is included in at least oneof a stop and start pattern of the presented optical code.
 15. Thedevice according to claim 13, wherein the pattern is included in a dataportion of the presented optical code.
 16. The device according to claim11, wherein the discriminating step includes the step of checking parityof a predetermined entity of the presented optical code, and thediscriminating step uses a result of the parity check.
 17. The deviceaccording to claim 16, wherein the algorithm further includes the stepof performing ink spread correction on the predetermined entity beforeperforming the step of checking parity.
 18. The device according toclaim 1, wherein the uncompensating step is performed using a firstpredetermined change, and when a result of the decoding the resultinguncompensated code step is invalid, performing the uncompensating stepwith a second predetermined number and performing the decoding theresulting uncompensated code step using the uncompensated code obtainedusing the second predetermined number.
 19. The device according to claim1, wherein: the uncompensating step is performed using at least firstand second respective predetermined changes; and the decoding theuncompensated code step includes the steps of: decoding respectiveresults of the uncompensating step for generating at least first andsecond corresponding decoded codes; and selecting a best decoded code ofthe generated at least first and second decoded codes.
 20. A decodermodule for decoding presented compensated optical codes having printedareas and spaces, wherein the decoder module includes softwareinstructions executable on a processor for performing an algorithmincluding the steps of: uncompensating the compensated optical code bycompensating for a predetermined adjustment in length of a dimension ofindividual spaces of the optical code without compensating for a changein the length of the dimension of individual printed areas of thecompensated optical code for generating an uncompensated optical code;and decoding the uncompensated optical code.
 21. The decoder moduleaccording to claim 20, wherein the uncompensating step includes the stepof normalizing the compensated optical code in accordance with a sum ofthe length of the dimension of the printed areas and spaces of thecompensated optical code.
 22. The decoder module according to claim 20,wherein the algorithm further includes the step of determining the valueof the predetermined adjustment from at least a portion of thecompensated code.
 23. The decoder module according to claim 20, whereinthe algorithm further includes the step of automatically discriminatinga presented compensated code from a presented uncompensated opticalcode.
 24. The decoder module according to claim 23, wherein thediscriminating step includes the step of recognizing a pattern of atleast a portion of the bars and spaces which indicates that thepresented optical code is a compensated optical code.
 25. A method fordecoding presented compensated optical codes having printed areas andspaces comprising the steps of: uncompensating a presented compensatedoptical code by compensating for a predetermined adjustment in length ofa dimension of individual spaces of the optical code withoutcompensating for a change in the length of the dimension of individualprinted areas of the compensated optical code for generating anuncompensated optical code; and decoding the uncompensated optical code.26. The method according to claim 25, wherein the uncompensating stepincludes normalizing the compensated optical code in accordance with asum of the length of the dimension of the printed areas and spaces ofthe compensated optical code.
 27. The method according to claim 25,further comprising the step of determining the value of thepredetermined adjustment from at least a portion of the compensatedcode.
 28. The method according to claim 25, further comprising the stepof discriminating a presented compensated code from a presenteduncompensated code.
 29. The method according to claim 28, wherein thediscriminating step includes recognizing a pattern of at least a portionof the bars and spaces which indicates that the presented optical codeis a compensated optical code.
 30. A module including softwareinstructions executable on a processor for performing the steps of:compensating an existing optical code having signals corresponding to asymbol having a pattern of spaces and printed areas which represents theexisting optical code, the device executing software instructions forperforming an algorithm including the steps of: determining a length ofa dimension of respective spaces of the symbol; and producing acompensated optical code that corresponds to a compensated symbol inwhich the length of the dimension of the respective spaces is adjustedby a predetermined length, while the length of the dimension ofrespective printed areas of the compensated symbol remains unchanged.31. The module according to claim 30, wherein the compensated opticalcode is provided to a printing device for printing a symbol representedby the compensated optical code.
 32. The module according to claim 30,wherein the compensating step is performed on a data portion of theoptical code.
 33. The module according to claim 30, wherein thecompensating step is performed only on a data portion of the opticalcode.
 34. The module according to claim 30, wherein the existing opticalcode is encoded with a bar code encodation scheme.
 35. The moduleaccording to claim 30, wherein the existing optical code is encoded withan n,k bar code encodation scheme, and wherein the predetermined lengthis a function of a module width of the resulting bar code symbol. 36.The module according to claim 30, wherein the algorithm furthercomprises the step of incorporating auto-discrimination code into thecompensated code to enable an optical code reader to discriminate thecompensated symbol which corresponds to the compensated optical codefrom the symbol which corresponds to the existing optical code symbol.37. The module according to claim 30, wherein the algorithm furthercomprises the step of incorporating a length indication into thecompensated code to indicate the predetermined length to enable anoptical reader to determine the predetermined length from thecompensated symbol.
 38. The module according to claim 30, wherein thepredetermined length is x modules, 0<x≦2.
 39. The module according toclaim 30, wherein the existing optical code is encoded with atwo-dimensional code encodation scheme which corresponds to atwo-dimensional symbol.
 40. The module according to claim 30, thealgorithm further comprising the step of dividing an encodation schemeof the existing optical code and resulting compensated optical code intoat least a first and a second set of data characters represented by atleast a portion of the pattern, wherein the first and second sets ofdata characters provide an auto-discrimination feature fordiscriminating compensated optical codes and existing optical codes, andwherein at least one of a symbol and a compensated symbol to bepresented to an optical reader include a pattern that is selected torepresent a data character from the first and second sets, respectively.41. The module according to claim 30, further comprising the step ofincluding at least one auto-discrimination feature in the compensatedoptical code to enable a reader to discriminate between compensatedoptical code and an existing optical code for the decoding thereof. 42.The module according to claim 41, wherein code symbols generatedaccording to an encodation scheme of the existing optical code have anexisting first start pattern and an existing first stop pattern, thestep of including at least one auto-discrimination feature comprising atleast one of: (a) using a second start pattern in place of the existingfirst start pattern in the compensated symbol, and (b) using a secondstop pattern in place of the existing stop pattern in the compensatedsymbol.
 43. The module according to claim 41, wherein symbolscorresponding to an encodation scheme of the existing optical code havea first finder pattern and wherein the step of including at least oneauto-discrimination feature comprises providing a second finder patternin the compensated symbol in place of the first finder pattern.
 44. Themodule according to claim 30, further comprising the step of including apattern in the compensated symbol to identify the compensated symbol ascorresponding to a compensated optical code.
 45. A method of producingan ink-spread compensated variant of an existing optical code encodationscheme comprising the steps of: determining a pattern of printed areasand spaces in the existing encodation scheme for a data input; theprinted areas and spaces each having a respective length in at least onedimension as a function of a given unit length for encoding information;and adjusting the length of respective spaces by a predetermined lengthwhile the length of respective printed area remains unchanged to producea modified code symbol.
 46. The method according to claim 45, furthercomprising the steps of: dividing the encodation scheme into at least afirst and a second set of data characters; and the step of determiningselecting the pattern from the second set, the different characters inthe first and second sets providing an auto-discrimination feature toidentify an ink-spread compensated code symbol.
 47. The method accordingto claim 45, further comprising the step of including at least oneauto-discrimination feature in the modified code symbol to enable areader to determine that the modified code symbol is an ink-spreadcompensated variant for the decoding thereof.
 48. The method accordingto claim 47, wherein code symbols generated according to the existingoptical code encodation scheme have an existing first start pattern andan existing first stop pattern, the step of including at least oneauto-discrimination feature comprising at least one of: (a) using asecond start pattern in place of the existing first start pattern in themodified code symbol; and (b) using a second stop pattern in place ofthe existing stop pattern in the modified code symbol.
 49. The methodaccording to claim 47, wherein code symbols generated according to theexisting optical code encodation scheme have a first finder pattern andwherein the step of including at least one auto-discrimination featurecomprises providing a second finder pattern in the modified code symbolin place of the first finder pattern.
 50. The method according to claim45, further comprising the step of including in the modified code symbola value of the magnitude of the predetermined length to enable a readerto determine the magnitude of the predetermined length for the decodingof the modified code symbol.
 51. The method according to claim 45,further comprising the step of including a data character pattern in themodified code symbol to identify the modified code symbol as anink-spread compensated variant.